#1
OK so i'm going nuts here

-I have 1 extremely noisy Fender Twin amp. Not the Twin Reverb, but the Twin Amp. Especially the reverb tank has a very bad hum that gets worse when you crank up the reverb level. I kind of gotten used to the noise and forgot about it until today.

Today i took a patch cable and connected 2 outputs on the back of the amp.

1. FX Send
2. Pre-amp OUT

This cleaned up the noise and hum for about 80%! I'm very happy, but i'm also having a hard time to understand why on earth this would even work? It also works if i connect the Pre-amp OUT to something like my synth.

Can someone make any sense out of this? Why is this working and can i damage the amp this way? Do i need to call ghostbusters? Is my amp possessed?
#2
I'm not sure I have the right schematic but all I can say is don't do this. According to my diagram you're feeding the preamp output into the output of the effect loop Send amp and at the same time into the input of the Return amp.

If you want to quiet the amp, look into lead dressing and shielding/star-grounding. Or have a competent amp tech do it. I don't know what the consequences of what you are doing would be, but I wouldn't risk it. People don't just go around plugging one output into another output...
#3
Quote by Invader Jim
I'm not sure I have the right schematic but all I can say is don't do this. According to my diagram you're feeding the preamp output into the output of the effect loop Send amp and at the same time into the input of the Return amp.

If you want to quiet the amp, look into lead dressing and shielding/star-grounding. Or have a competent amp tech do it. I don't know what the consequences of what you are doing would be, but I wouldn't risk it. People don't just go around plugging one output into another output...

I'll look into that. Well i wasn't going to leave it like this, i was just trying to find out what worked. And this worked, and i am completely stumped why this works. You are almost right btw. The return is not in use. So just Send -> Pre-Out. And that's it, even makes the reverb hum go away.

Out of curiosity.. what can you actually damage by routing an output into an output. Won't that just cancel each other?
#4
That's not how outputs work. Would you take a double male power cord and pug both ends into two different electrical outlets? Would you expect them to cancel each other out? I hope not.

Anyway, I don't see how this specific case would damage your amp, as preamp signals aren't generally large enough to cause any damage and you could cascade basically anything into anything else at that point. But Jim's right in principle, it's a bad idea to just run around plugging things into other things when you have no idea what they do.

I'll take a look at a schematic later today and post if I see anything obvious, but this should probably go to a tech.
#5
Quote by GotStrings
I'll look into that. Well i wasn't going to leave it like this, i was just trying to find out what worked. And this worked, and i am completely stumped why this works. You are almost right btw. The return is not in use. So just Send -> Pre-Out. And that's it, even makes the reverb hum go away.

Out of curiosity.. what can you actually damage by routing an output into an output. Won't that just cancel each other?

The send and return in this amp are always connected internally unless there is a plug in the return jack.

The second question is too hard for me to explain. I know that sounds like a cop-out but, unlike a lot of people, I'm not shy about admitting when I don't know something. Like I said earlier, I am not sure what the consequences would be in this case. I am ok at a lot of stuff instead of being really great at a couple of things.
#6
Thanks guys!

Well, the thing is in this town there's only one shitty little local music shop, people there can't even tell the difference between a green and a blue pick. So they can't fix it, they could send it somewhere i guess. But that's pricy stuff. So if this workaround works, and it's safe without damaging anything, i am thinking of using it.

Still seriously wondering why on earth it works. I just tried adding the PRE-out to the output of my digital piano, and synth. Leaving those devices off. And also that got rid of the noise. I'm really stumped.
#7
I'm not sure what the purpose of having both of those jacks is, aren't they the same thing?
Sounds like maybe part of the pre-amp is ungrounded, and by connecting it to another piece you ground it. What happens if you patch the Pre-amp out to the power amp in, or effects return? I imagine that would make a little more sense than plugging two inputs into each other.

But if it's that easy to solve your noise problem, I can't think of a way that connecting line-level outputs would really hurt for now...


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#8
Ok, I took a look at the schematic. I agree with the above assessment - you've got a bad connection somewhere and all you're doing is switching the preamp out jack by plugging it in. It's in parallel with the power amp in jack, so if the theory is correct all you should need to do is have a shorted plug in the preamp out jack. The safe and obvious way to do this if you don't have a shorted jack or don't want to make one is to plug the preamp out into the power amp in.

The other methods won't cause any harm but they also don't make any sense to do.
#9
Thanks!!

Did a little test, while keeping the Pre-OUT where it is i connected the other end of the cable to:

Return: Same amount of noise as before
Send: No noise, great clean amp
Power In: Same amount of noise as before; when i unplug the pre-out and keep the plug in "Power amp In" the noise get's a lot worse. So this could indicate something?

Return -> Send: Same amount of noise.

So i guess it's fair to say there is something wrong with either the pre-out and/or fx send?

I haven't tried the shortened jack yet.
Last edited by GotStrings at Dec 21, 2013,